Insights into Spt6: a histone chaperone that functions in transcription, DNA replication, and genome stability

A conserved function of corepressors is to nucleate assembly of the transcriptional preinitiation complex

“…In ScSpt6, the YqgF domain was required for repression, but not the tSH2 domain (Figure 4K, Figure S9F). The YqgF domain has recently been implicated in initiation of transcription, as mutant forms lacking this domain are trapped at the TSS in Arabidopsis 37 , while the tSH2 domain is well documented as being a Pol-II interaction surface 27 . We then mapped the location of these domains onto the protein complex formed between RNA POL II subunits, DNA, PAF complex, and SPT or DSIF proteins as in Figure 4H 30 .…”

“…While SPT4, SPT5 and SPT6 are best known for their roles in transcriptional elongation 27,30,[78][79][80] and proximal promoter pausing in metazoans [81][82][83] , they were originally identified as yeast mutants that were able to restore transcription at a locus with a promoter disrupted by the Ty transposon 32 . The Suppressor of Ty genetic screen identified many core components of the transcriptional machinery, including: histones, TBP, Mediator15, as well as components of SAGA and FACT complexes 84 .…”

“…Our observation that loss of SPT4, SPT5 and SPT6 activity resulted in a loss of repression led us to hypothesize that some complexes containing these components must be required for this repressive function. Both SPT5 and SPT6 are multidomain proteins that make extensive contacts with both RNA Pol II and other complexes 26,27 . We engineered targeted deletions in both SPT5 and SPT6 in selected domains to determine which may be required for this newly found repressive function (Figure 4A,J,K).…”

“…During transcriptional pausing, Poll II initiates transcription but then stalls as a result of a metazoan-specific protein called Negative Elongation Factor (NELF) interacting with the DRB Sensitivity Inducing Factor (DSIF) complex. The DSIF components SPT4 and SPT5 are conserved across eukaryotes 26 , and in concert with SPT6 27 , are crucial elongation factors that are associated with Pol-II at all points during transcriptional activation and elongation [28][29][30][31] . While these factors are best known for their roles in elongation and pausing, they were originally identified in yeast as factors critical for promoter identification and transcriptional initiation 32,33 .…”